1. Field of the Invention
The present invention relates to an inkjet recording apparatus, or to technology for maintaining and cleaning discharge surface nozzles of industrial-use droplet discharge devices or the like.
2. Description of the Related Art
In recent years, inkjet recording apparatuses (inkjet printers) serving as recording apparatuses that print/record images or the like taken by digital still camera have become widely distributed. Inkjet recording apparatuses have a plurality of recording elements in the head, the recording head is moved to scan the recording medium while ink droplets are discharged from the recording elements to the recording medium, the recording medium is conveyed by a single line when one line of image has been recorded on recording paper, and an image is formed on the recording paper by repeating these steps.
There are inkjet printers that use a short serial head and record images while causing the head to scan in the width direction of the recording medium, or those that use a line head in which recording elements are arrayed across the entire range of one side of the recording medium. In printers in which a line head is used, images can be recorded on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the array direction of the recording elements. In printers in which a line head is used, a carriage or another conveyance system for moving the short head back and forth is unnecessary, and complex scanning control for the carriage movement and recording medium is not required. Also, the recording medium alone moves, so recording speed can be increased in comparison with printers in which a serial head is used.
In inkjet printers, when ink and other dirt deposited on the nozzle surface (the surface of the print head facing the recording surface, on which nozzle openings are formed), the result is not only nozzle discharge defects (principally abnormal flight direction of the ink droplets), but also contamination of the recorded image with this dirt.
Therefore, a variety of cleaning methods have been proposed for removing ink, paper dust, and other dirt deposited on the nozzle surface.
Also, water-repelling treatment has been performed on the nozzle surface to keep surface wettability uniform, so the liquid part of the ink deposited on the nozzle surface can be relatively easily removed, but it is still difficult to completely remove solidified ink, paper dust from the recording paper, and other types of dirt. As a result, these types of dirt on the nozzle surfaces cause the quality of the recorded image to be degraded, and therefore require to be dealt with.
On the other hand, ink has a characteristic in that its viscosity increases due to moisture evaporation when the ink is in contact with the atmosphere, eventually resulting in hardening; and this higher-viscosity ink (thickened ink) is also the cause of discharge defects in the nozzles (principally abnormal discharge amounts and non-discharge), and the recorded image may be degraded.
Conventionally, known methods for cleaning a nozzle surface include a method for wiping dirt deposited on the nozzle surface using a blade or the like. Also, methods for removing higher-viscosity ink include a method in which a dummy discharge (liquid discharge) of ink is made to a cap or the like at regular intervals.
In the inkjet recording apparatus disclosed in Japanese Patent Application Publication No. 11-342621, there is proposed a wiping mechanism that performs surface wiping action by causing a roller that is shorter in length than the head array to rotate and move in the nozzle array direction, and the wiping mechanism cleans while eliminating wiping marks on the nozzle surface by imparting a uniform pressure to the nozzle surface.
The image forming method and apparatus thereof cited in Japanese Patent Application Publication No. 11-170566 has a step of performing a preliminary discharge, a step of wiping deposited liquids, and a step of wiping deposited liquids after image formation; and removal of thickened ink and adhered ink is efficiently performed using a rotating cleaning roller and an elastic blade whose external peripheral surfaces are pressed to the head as the cleaning roller and elastic blade move relatively across the head.
Nevertheless, in the above method for cleaning a nozzle surface, the entire surface of the nozzle cannot always be uniformly cleaned. A drawback is that applying a force to the deposited matter is sometimes insufficient and the deposited matter cannot be removed. If a strong force is applied to the deposited matter, the cleaning member, the nozzle surface as such, or the nozzle surface treated with a water repellent, and other such surface-treated layers, may be damaged by the friction force generated between the nozzle surface and the cleaning member.
There is a drawback in that when dummy discharge is frequency performed to remove thickened ink in the vicinity of the discharge port, more ink is consumed.
In the inkjet recording apparatus disclosed in Japanese Patent Application Publication No. 11-342621, dry wiping takes place in the initial state of the wiping step, and the durable lifespan of the layer treated with an ink repellent on the nozzle surface is reduced.
By periodically performing preliminary discharges, the image forming method and apparatus thereof cited in Japanese Patent Application Publication No. 11-170566 circumvents a known problem in conventional inkjet technology whereby non-discharge is caused by the formation of a discharge film produced by thickened ink on the meniscus surface when the head is left in a inactive state in which no ink is discharged.